Screw compressor

ABSTRACT

In order to obtain a screw compressor which is small in size and weight and has ease of maintenance and high reliability, the screw compressor comprises a screw rotor, a low-pressure-side bearing and a high-pressure-side bearing which support the screw rotor, a motor which drives the screw rotor, a motor casing which accommodates the motor, a main casing which accommodates the screw rotor and the low-pressure-side bearing, and a discharge casing which accommodates the high-pressure-side bearing. The motor casing, the main casing, and the discharge casing are accommodated in a steel pipe chamber, and the steel pipe chamber includes a low-pressure-side chamber and a high-pressure-side chamber which are able to be divided in the axial direction. By using a flange provided on an inner surface of the steel pipe chamber, a flange provided in the main casing, and a sealing component provided between the flanges, the steel pipe chamber is divided into a low-pressure-side space and a high-pressure-side space.

FIELD OF THE INVENTION

The present invention relates to a screw compressor which compresses a fluid, and particularly, to a screw compressor which is used in a refrigeration cycle of an air conditioner, a refrigerating machine, or the like.

DESCRIPTION OF RELATED ART

In a screw compressor, a screw rotor having a three-dimensionally twisted curved surface is provided as a compression mechanism portion. For this reason, generally, a casing accommodating the compression mechanism portion is made from cast iron which is able to be formed in a complex shape. The cast iron generally used for the casing of the compressor has strength lower than that of steel for pressure pipe. In the case where a design pressure is the same, the cast iron casing needs to be thicker than the steel casing. For this reason, there is a problem in that the mass of the compressor increases. In addition, in the screw compressor, lubricant contained in a discharge gas needs to be separated. For this reason, in many cases, an oil separator is integrally formed with the compressor. At this time, since the oil separator is also made from cast iron, there is a problem in that the mass of the compressor largely increases.

Meanwhile, in order to decrease the size and weight of the screw compressor, a method may be supposed in which a compression mechanism portion is accommodated in a steel pipe chamber as in a rotary compressor or a scroll compressor. For example, in U.S. Pat. No. 4,545,742, a structure is disclosed in which a compression mechanism portion of a screw compressor is accommodated in a steel pipe chamber. In this related art, a configuration is adopted in which a pressure inside the steel pipe chamber is set to a high pressure.

In addition, in another related art, a screw compressor is supposed in which a cast iron compression mechanism portion is accommodated in a steel pipe chamber, and different types of metals, that is, the cast iron and the steel pipe are welded to each other so as to divide the inside of the steel pipe chamber into a low pressure portion and a high pressure portion.

When the steel pipe chamber is adopted in the screw compressor, it is possible to realize a decrease in size and weight. However, the screw compressors of the related art have the following problems.

In the case where the pressure inside the steel pipe chamber is raised to a high pressure after compressing a refrigerant gas, a motor is cooled by a high-temperature and high-pressure refrigerant gas. Due to this, there is a problem in that the motor may be overheated during an operation of the compressor, and the reliability thereof is not satisfactory. On the contrary, the pressure inside the steel pipe chamber may be dropped to a low pressure before compressing the refrigerant gas. However, in the configuration in which the pressure inside of the steel pipe chamber is dropped to a low pressure, it is difficult to install an oil separator in the steel pipe chamber. For this reason, it is necessary to install the oil separator separately from the compressor, and hence there is a problem in that the entire compressor increases in size.

In addition, in the case of the structure in which different types of metals, that is, the steel pipe and the cast iron are welded to each other so as to obtain the low pressure portion and the high pressure portion divided from each other, the different types of metals can be welded to each other, but when the optimal welding condition is not set, cracks occur due to the insufficient welding penetration of the welded portion, and then a gas leakage or a leakage of a high-pressure refrigerant gas to the low pressure portion occurs, which causes a problem in that the performance thereof is degraded. In addition, in this structure, since it is necessary to weld the entire circumference of the steel pipe chamber so as to form the low pressure portion and the high pressure portion divided from each other, the weld length is long. For this reason, there is a problem in that a potential of causing cracks in the welded portion increases, and this structure is difficult to be applied to a high capacity compressor. In addition, when this structure is adopted, the compressor becomes a hermetic structure, and hence there is a problem in that maintenance such as an exchange of a bearing cannot be performed.

As described above, in the structure in which the steel pipe chamber accommodates the compression mechanism portion of the screw compressor, it is difficult to dispose the motor on the low pressure side and to dispose the oil separator on the high pressure side after making the compressor in a semi-hermetic state. That is, although the steel pipe chamber structure is a remarkable structure in small size and weight, there is a problem in that ease of maintenance and reliability are degraded.

SUMMARY OF THE INVENTION

An object of the invention is to obtain a screw compressor which is small in size and weight and has ease of maintenance and high reliability.

In order to attain the above-described object, according to an aspect of the invention, there is provided a screw compressor including: a screw rotor which includes a toothed portion and a shaft portion; a low-pressure-side bearing and a high-pressure-side bearing which support the shaft portion of the screw rotor; a driving motor which is directly connected to the shaft portion of the screw rotor; a motor casing which accommodates the motor; a main casing which accommodates the screw rotor and the low-pressure-side bearing; a discharge casing which accommodates the high-pressure-side bearing of the screw rotor; and a steel pipe chamber which accommodates the motor casing, the main casing, and the discharge casing, wherein the steel pipe chamber includes a low-pressure-side chamber and a high-pressure-side chamber which are able to be divided in the axial direction, and wherein a space inside the steel pipe chamber is divided into a low-pressure-side space and a high-pressure-side space through a flange provided in an inner surface of the steel pipe chamber, a flange provided in the main casing or the motor casing, and a sealing component provided between the flanges.

Here, the low-pressure-side chamber and the high-pressure-side chamber may be connected to each other through flanges provided in outer-surface ends thereof, so that the inside of the steel pipe chamber is sealed from an ambient air. The high-pressure-side chamber may be further divided into two parts in the axial direction so as to form a first high-pressure-side chamber connected to the low-pressure-side chamber and a second high-pressure-side chamber connected to the first high-pressure-side chamber, and the first and second high-pressure-side chambers may be preferably connected to each other through flanges provided in outer-surface ends thereof, so that the inside of the steel pipe chamber is sealed from the ambient air.

In addition, the flange provided on the inner surface of the high-pressure-side chamber may be connected to the flange provided in the main casing through the sealing component, the flange provided in the inner surface of the high-pressure-side chamber may be connected to the flange provided in the motor casing through the sealing component, the flange provided on the inner surface of the low-pressure-side chamber may be connected to the flange provided in the main casing through the sealing component, or the flange provided on the inner surface of the low-pressure-side chamber is connected to the flange provided in the motor casing through the sealing component, so that the space inside the steel pipe chamber is divided into the low-pressure-side space and the high-pressure-side space.

A central axis of a shell constituting the steel pipe chamber may be preferably disposed in the horizontal direction.

The screw rotor according to the invention may preferably include at least a pair of male and female rotors meshing with each other. In addition, when as an operation fluid to be compressed in the compressor according to the invention, which is a refrigerant used in a refrigeration cycle, a refrigerant having a cooling ability per unit volume flow rate equal to or less than 70% of R407C is used, the number of teeth of the male rotor of the screw rotor is set to four, the number of teeth of the female rotor thereof is set to six, and then the driving motor directly connected to the male rotor is driven by an inverter, it is possible to use a refrigerant (a low GWP refrigerant) having a low global warming potential.

In addition, a central axis of the steel pipe chamber may be disposed between a central axis of the male rotor and a central axis of the female rotor.

Further, the screw compressor may further be applied to one including a gate rotor which meshes with the screw rotor; and a bearing which supports a shaft portion of the gate rotor.

According to another aspect of the invention, there is provided a screw compressor including: a screw rotor which includes a toothed portion and a shaft portion; a gate rotor which meshes with the screw rotor; a low-pressure-side bearing and a high-pressure-side bearing which support the shaft portion of the screw rotor; a bearing which supports a shaft portion of the gate rotor; a driving motor which is directly connected to the shaft portion of the screw rotor and drives the screw rotor; a motor casing which accommodates the motor; a main casing which accommodates the screw rotor and the gate rotor; and a steel pipe chamber which accommodates the motor casing and the main casing, wherein the steel pipe chamber includes a low-pressure-side chamber and a high-pressure-side chamber which are able to be divided in the axial direction, and wherein a space inside the steel pipe chamber is divided into a low-pressure-side space and a high-pressure-side space through a flange provided on an inner surface of the steel pipe chamber, a flange provided in the main casing or the motor casing, and a sealing component provided between the flanges.

According to still another aspect of the invention, there is provided a screw compressor including: a screw rotor; a bearing which supports the screw rotor; a motor which drives the screw rotor; a motor casing which accommodates the motor; a main casing which accommodates the screw rotor; and a steel pipe chamber which accommodates the motor casing and the main casing, wherein the steel pipe chamber is able to be divided in the axial direction, and wherein a space inside the steel pipe chamber which is able to be divided is divided into a low-pressure-side space and a high-pressure-side space through a sealing component.

According to the invention, since the steel pipe chamber accommodating the motor casing and the main casing is provided, the steel pipe chamber is able to be divided in the axial direction, and the space inside the steel pipe chamber which is able to be divided is divided into the low-pressure-side space and the high-pressure-side space through the sealing component, it is possible to obtain a screw compressor which is small in size and weight and has ease of maintenance and high reliability.

Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a vertical sectional view of a screw compressor according to a first embodiment of the invention.

FIG. 2 is a vertical sectional view of a screw compressor according to a second embodiment of the invention.

FIG. 3 is a vertical sectional view of a screw compressor according to a third embodiment of the invention.

FIG. 4 is a vertical sectional view of a screw compressor according to a fourth embodiment of the invention.

FIG. 5 is a vertical sectional view of a screw compressor according to a fifth embodiment of the invention.

FIG. 6 is a plan sectional view of a screw compressor according to a sixth embodiment of the invention.

FIG. 7 is a plan sectional view of a screw compressor according to a seventh embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, the specific embodiments of the invention will be described by referring to the drawings. In the respective drawings, the same reference numerals are given to the same and equivalent constituents.

First Embodiment

FIG. 1 shows a first embodiment according to the invention. In the following description, although a twin screw compressor having two male and female screw rotors are exemplified as the embodiment, the invention is not limited to the twin screw compressor, but may be also applied to a single screw compressor having one screw rotor.

As shown in FIG. 1, a screw compressor includes a motor casing 1, a main casing 2, and a discharge casing 3 which are connected to each other. The motor casing 1 accommodates a driving motor 4 which drives a compression mechanism portion, and is fixed to the main casing 2 through means such as bolts. The main casing 2 is provided with a cylindrical bore 5 and a suction port 6 which introduces a refrigerant gas into the cylindrical bore 5. The cylindrical bore 5 accommodates a female rotor (not shown) and a male rotor 14, rotatably supported by roller bearings 7, 8, and 9 (the low-pressure-side bearings 7 and 8 and the high-pressure-side bearing 9) and a ball bearing 12 (the high-pressure-side bearing), so as to mesh the rotors with each other, and a shaft portion of the male rotor 14 is directly connected to the motor 4. The discharge casing 3 accommodates the roller bearing 9 and the ball bearing 12 (the high-pressure-side bearings), and the bearings are fixed to the main casing 2 through means such as bolts. In addition, one end of the discharge casing 3 is attached with a closure plate 17 which closes a bearing chamber 16 for accommodating the roller bearing 9 and the ball bearing 12.

Oil feeding channels 18 and 19 are formed inside the main casing 2 and the discharge casing 3 so as to allow an oil storage tank 20 provided in the lower portions of high-pressure-side chambers 22 and 23 to communicate with the above-described bearings.

The motor casing 1, the main casing 2, and the discharge casing 3 are accommodated in a steel pipe chamber which is adapted to be divided in the axial direction. The steel pipe chamber includes a low-pressure-side chamber 21 and the high-pressure-side chambers 22 and 23. When flanges 24, 25, 26, and 27 formed in outer-surface ends of the chambers are connected to each other through means such as bolts together with sealing components (not shown), it is possible to seal the inside of the steel pipe chamber from the ambient air, and to obtain a structure in which the steel pipe chamber is able to be divided in the axial direction. The high-pressure-side chambers are formed to be divided into two parts in the axial direction so as to include the first high-pressure-side chamber 22 which is connected to the low-pressure-side chamber and the second high-pressure-side chamber 23 which is connected to the first high-pressure-side chamber 22.

The flange 29 formed in the main casing 2 and the flange 28 formed inside the high-pressure-side chamber 22 are connected through bolts with a sealing component 30 interposed therebetween. Accordingly, spaces 31 and 32 inside the steel pipe chamber are divided into the space 31 defined as a low-pressure-side space, and the space 32 defined as a high-pressure-side space.

Next, the streams of the refrigerant gas and the oil will be described.

The foreign materials in the low-temperature and low-pressure refrigerant gas sucked from a suction port 33 provided in the low-pressure-side chamber 21 are collected by a strainer 34, and then, the refrigerant gas passes through a gas channel provided between the motor 4 and the motor casing 1 and an air gap between a stator 4 a and a rotor 4 b of the motor so as to cool the motor 4. The refrigerant gas used for the cooling operation is sucked from a suction port 6 formed in the main casing 2 to a suction chamber formed by the main casing 2 and meshing tooth surfaces of the male and female screw rotors. Subsequently, the refrigerant gas is hermetically sealed in a compression chamber formed by the main casing 2 and the meshing tooth surfaces of the male and female screw rotors in accordance with the rotation of the male rotor 14 connected to the motor 4, and is gradually compressed in accordance with the contraction of the compression chamber, so that the refrigerant gas becomes a high-temperature and high-pressure gas. The compressed refrigerant gas passes through a discharge channel 35 and a discharge pipe 36 formed in the discharge casing 3, and is discharged toward an end cover 37 constituting the high-pressure-side chamber 23.

During the compression operation, a radial load of a compression reaction force acting on the male and female screw rotors is supported by the roller bearings 7, 8, and 9, and a thrust load thereof is supported by the ball bearing 12. By means of a differential pressure, an oil used for cooling and lubricating the bearings is fed from the oil storage tank 20 provided in the lower portions of the high-pressure-side chambers 22 and 23 via the oil feeding channels 18 and 19 communicating with each of the bearings. The oil used for the oil feeding operation is discharged to the end cover 37 constituting the high-pressure-side chamber 23 together with the compressed refrigerant gas. The oil contained in the compressed refrigerant gas is first separated by the collision with the end cover 37, is secondarily separated by a collection oil separator such as a demister 38 installed in the high-pressure-side chamber 23, and is collected in the oil storage tank 20 provided in the lower portions of the high-pressure-side chambers 22 and 23. The compressed refrigerant gas passes through a gas channel 39 of the upper portion of the high-pressure-side chamber 22, and is discharged through a discharge port 40 provided in the high-pressure-side chamber 22.

In the screw compressor of the related art, the motor casing 1, the main casing 2, and the discharge casing 3 are connected to each other so as to be sealed, and serve as a pressure-resistant casing which maintains the internal pressure. Meanwhile, the screw compressor is formed into a complex casing structure so as to accommodate a volume control slide valve or a screw rotor having a three-dimensionally twisted complex curved surface. For this reason, generally, the casing of the screw compressor is made from cast iron which is able to be formed in a complex shape. In the case where the casing is made from cast iron, since the strength is lower than that of steel for a pressure pipe, the thickness of the casing needs to be increased in order to maintain the strength, and hence there is a tendency that the mass of the compressor increases. On the contrary, in the structure of the embodiment, since the internal pressure is maintained by the steel pipe chamber, the main casing 2 made from cast iron is mainly used to accommodate the compression mechanism portion. Accordingly, it is possible to minimize the mass of the cast iron, and to obtain a screw compressor which is small in size and weight.

In addition, in the embodiment of FIG. 1, the central axis of the shell constituting the steel pipe chamber is disposed in the horizontal direction. In the case where the steel pipe chamber is disposed in the horizontal direction, since the low center of gravity is realized, it is possible to obtain excellent safety when the compressor is carried in or out. However, the invention is not limited to the case in which the steel pipe chamber is disposed in the horizontal direction, but even when the central axis of the shell constituting the steel pipe chamber is disposed in the vertical direction, it is possible to minimize the mass of the cast iron casing used for accommodating the compression mechanism portion.

The screw compressor of the related art in which the cast iron casing is accommodated in the steel pipe chamber has a structure in which the pressure inside the steel pipe chamber is set to the low pressure before compressing the refrigerant gas or the high pressure after compressing the refrigerant gas or a structure in which different types of metals, that is, the steel pipe and the cast iron are welded to each other so as to form divided high-pressure and low pressure chambers.

In the case where the inside of the steel pipe chamber is set to the low pressure, since the refrigerant gas compressed by the screw rotor needs to be immediately discharged to the outside of the steel pipe chamber, it is difficult to install the oil separator in the inside of the steel pipe chamber. For this reason, it is necessary to separately install the oil separator, and it is difficult to realize a compact in size.

In the case where the inside of the steel pipe chamber is set to the high pressure, since the driving motor 4 is cooled by the high-pressure and high-temperature refrigerant gas, and the driving motor 4 is overheated during the operation of the compressor, there is a problem in that the reliability is not satisfactory. In addition, although an insulation member of the driving motor 4 is made from a resin material, it is necessary to increase the heat-resistant grade of the resin material.

In the case where different types of metals are welded to each other so as to form divided high pressure chamber and low pressure chamber, when the welding condition is not optimally set, cracks occur in the welded portion between the different types of metals due to the insufficient welding penetration, and the high-pressure refrigerant gas leaks to the low pressure portion, so that the performance thereof is degraded. In addition, in order to form the high pressure chamber and the low pressure chamber which are divided from each other, since it necessary to weld the entire circumference of the steel pipe chamber, the weld length is long. Particularly, the weld length becomes longer as the capacity of the compressor increases. The high-pressure refrigerant gas leaks to the low pressure portion, so that the danger thereof increases. For this reason, this structure is not suitable for a large capacity compressor.

On the contrary, in the structure of the embodiment, since the inside of the steel pipe chamber is divided into the high-pressure space and the low-pressure space through the sealing component 30, it is possible to dispose the driving motor 4 in a position on the low pressure side of the inside of the steel pipe chamber, and to dispose the oil separator in a position on the high pressure side of the inside of the steel pipe chamber. With such a configuration, it is possible to cool the motor 4 using the low-pressure and low-temperature refrigerant gas, and to dispose the oil separator in the inside of the steel pipe chamber.

In the embodiment, as the oil separator, both the collision-type oil separation using the end cover 37 and the collection-type oil separation using the demister 38 are used. In addition, since the low pressure portion and the high pressure portion are divided by the sealing component 30, the airtightness is excellent, and the possibility that the performance is degraded due to the leakage of the high-pressure refrigerant gas to the low pressure portion is extremely small. In addition, since it is possible to divide the steel pipe chamber into the low-pressure-side chamber 21 and the high-pressure-side chambers 22 and 23, it is possible to easily perform maintenance such as the exchange of the bearing.

Second Embodiment

FIG. 2 shows a second embodiment according to the invention. As in the embodiment of FIG. 1, the steel pipe chamber includes the low-pressure-side chamber 21 and the high-pressure-side chambers 22 and 23. Since the flanges 24, 25, 26, and 27 formed in the chambers are connected to each other through means such as bolts, the low-pressure-side chamber 21 and the high-pressure-side chambers 22 and 23 are sealed from each other, are sealed from the ambient air, and are able to be divided.

The embodiment is different from the first embodiment in that the flange 29 formed in the motor casing 1 and the flange 28 formed inside the high-pressure-side chamber 22 are connected to each other through bolts with the sealing component 30 interposed therebetween. Even in the embodiment, the spaces 31 and 32 inside the steel pipe chamber are divided into the space 31 as the low-pressure-side space and the space 32 as the high-pressure-side space. Additionally, it is possible to cool the driving motor 4 by using the low-pressure and low-temperature refrigerant gas, and to dispose the oil separator in the inside of the steel pipe chamber. Further, it is possible to obtain the excellent airtightness between the low pressure portion and the high pressure portion, and to easily perform maintenance.

Third Embodiment

FIG. 3 shows a third embodiment according to the invention. As in the embodiment of FIG. 1, the steel pipe chamber includes the low-pressure-side chamber 21 and the high-pressure-side chamber 22. In addition, the flanges 24 and 25 formed in the chambers are connected to each other through means such as bolts so as to be sealed from each other, and are able to be divided. In the embodiment, the flange 29 formed in the main casing 2 and the flange 28 formed in the inside of the low-pressure-side chamber 21 are connected to each other through bolts with the sealing component 30 interposed therebetween. The spaces 31 and 32 inside the steel pipe chamber is divided into the space 31 as the low-pressure-side space and the space 32 as the high-pressure-side space. Even in the embodiment, it is possible to cool the driving motor 4 by using the low-pressure and low-temperature refrigerant gas, and to dispose the oil separator in the inside of the steel pipe chamber. Further, it is possible to obtain the excellent airtightness between the low pressure portion and the high pressure portion, and to easily perform maintenance.

In addition, in the embodiment, since it is possible to disassemble and/or assemble the compressor without dividing the high-pressure-side chamber 22, it is not necessary to provide the sealing component or the flange used for connecting the high-pressure-side chambers. Accordingly, there is an advantage in that it is possible to obtain the compressor which is more simplified and reliable compared with the embodiment in which the high-pressure-side chamber 22 needs to be divided.

Fourth Embodiment

FIG. 4 shows a fourth embodiment according to the invention. As in the embodiment of FIG. 1, the steel pipe chamber includes the low-pressure-side chamber 21 and the high-pressure-side chamber 22. In addition, the flanges 24 and 25 formed in the chambers are connected to each other through means such as bolts so as to be sealed from each other, and are able to be divided. The embodiment is different from the above-described embodiments in that the flange 29 formed in the motor casing 1 and the flange 28 formed in the inside of the low-pressure-side chamber 21 are connected to each other through bolts with the sealing component 30 interposed therebetween. Even in the embodiment, the spaces 31 and 32 inside the steel pipe chamber is divided into the space 31 as the low-pressure-side space and the space 32 as the high-pressure-side space. Accordingly, it is possible to cool the driving motor 4 by using the low-pressure and low-temperature refrigerant gas, and to dispose the oil separator in the inside of the steel pipe chamber. Further, it is possible to obtain the excellent airtightness between the low pressure portion and the high pressure portion, and to easily perform maintenance. In addition, even in the embodiment, as in the third embodiment, since it is possible to disassemble and/or assemble the compressor without dividing the high-pressure-side chamber 22, it is not necessary to provide the sealing component between the high-pressure-side chambers required when the high-pressure-side chamber 22 is divided.

Fifth Embodiment

FIG. 5 shows a fifth embodiment according to the invention. As in the embodiment of FIG. 1, the steel pipe chamber includes the low-pressure-side chamber 21 and the high-pressure-side chambers 22 and 23. Since the flanges 24, 25, 26, and 27 formed in the chambers are connected to each other through means such as bolts, the steel pipe chamber is able to be divided. In the embodiment, the flange 25 integrally formed with a shell 41 is disposed over both sides, that is, an ambient air side 25 a of the shell 41 and a refrigerant side 25 b thereof. In the embodiment, since it is not necessary to further install a flange used for the connection to the casing in the inside of the shell 41, it is possible to divide the inside of the steel pipe chamber into the low-pressure-side space 31 and the high-pressure-side space 32 in a more simplified structure.

In addition, in the embodiment, the flange 29 formed in the main casing 2 and the flange 25 formed in the high-pressure-side chamber 22 are connected to each other through bolts, but even in the configuration in which the flange formed in the motor casing is connected to the flange formed in the high-pressure-side chamber through bolts, the flange formed in the main casing is connected to the flange formed in the low-pressure-side chamber through bolts, or the flange formed in the motor casing is connected to the flange formed in the low-pressure-side chamber through bolts, it is possible to obtain the same advantages.

Sixth Embodiment

FIG. 6 shows a sixth embodiment according to the invention. As in the embodiment of FIG. 1, the motor casing 1, the main casing 2, and the discharge casing 3 are accommodated in the steel pipe chamber which are adapted to be divided. The embodiment is described as an example in which a refrigerant having a cooling ability for each fluid per unit volume flow rate equal to or less than 70% of a refrigerant R407C is used as an operation refrigerant to be compressed. In the embodiment, the screw rotor accommodated in the main casing 2 has a configuration in which the number of teeth of the male rotor 14 is set to four, and the number of teeth of the female rotor 15 is set to six, and the driving motor 4 directly connected to the shaft portion of the male rotor 14 is driven by an inverter 43 through the power supply terminal 42. A male rotor 14 is rotatably supported by roller bearings 7, 8 and 9, and a ball bearing 12. A female rotor 15 is rotatably supported by roller bearings 10 and 11, and a ball bearing 13.

As refrigerants used in an air conditioner or a refrigerating machine, there are many kinds of refrigerants such as R410A, R407C, R134 a, ammonia, and carbon dioxide, and they have different cooling abilities for each fluid per unit of volume. In the case where it is assumed that the cooling ability required for the air conditioner or the refrigerating machine is the same, when a refrigerant having a large cooling ability per unit volume is adopted, a theoretical discharge amount of the compressor becomes small, and hence it is possible to make the compressor decrease in size. On the contrary, when a refrigerant having a small cooling ability per unit volume is adopted, the compressor increases in size. For example, when the cooling ability per unit volume flow rate of the refrigerant R407C is set to 100, the refrigerant R410A is about 150, and the refrigerant R134 a is about 65. Thus, in the case of obtaining the same cooling ability, when the refrigerant R134 a is adopted, the compressor increases in size compared with the case adopting the R407C or R410A. Recently, a refrigerant (a low GWP refrigerant) having a low global warming potential has gained attention. The refrigerant generally has a small cooling ability per unit volume as in, for example, R134 a. However, according to the embodiment, even when the low GWP refrigerant is used, it is possible to realize a decrease in weight of the compressor.

As the number of teeth of the male rotor 14 and the female rotor 15 of the screw compressor, there are a combination of five and six and a combination of five and seven. However, in the case where the diameter of the rotor is the same, since the area of the tooth groove becomes large as the number of teeth becomes small, there is a tendency that the theoretical discharge amount increases. In the embodiment, even in the case where the refrigerant having a small cooling ability per unit volume flow rate is adopted, the number of teeth of the male rotor 14 and the female rotor 15 is set to a combination of four and six, and the driving motor 4 directly connected to the shaft portion of the male rotor 14 is driven by the inverter 43 so as to be accelerated. According to the embodiment, the compressor used with an external power supply 44 and driven at a constant speed can be remarkably decreased in size and weight.

Seventh Embodiment

FIG. 7 shows a seventh embodiment of the invention. As in the embodiment of FIG. 1, the motor casing 1, the main casing 2, and the discharge casing 3 are accommodated in the steel pipe chamber which is able to be divided. A central axis 47 of the steel pipe chamber is disposed between a central axis 45 of the male rotor 14 and the driving motor 4 directly connected to the male rotor 14, and a central axis 46 of the female rotor 15. In the twin screw compressor, the central axis of the male rotor 14 and the central axis of the female rotor 15 always exist. Since the central axis of the steel pipe chamber is disposed between two axes, it is possible to decrease a dead space inside the steel pipe chamber generated when the cast iron casing is disposed inside the steel pipe chamber, and thus to further decrease the size of the screw compressor.

In addition, in the above-described embodiments, the twin screw compressor is exemplified, but the invention may be also applied to the single screw compressor. When the single screw compressor is exemplified, the single screw compressor is provided with a screw rotor which includes a toothed portion and a shaft portion, a gate rotor which meshes with the screw rotor, a low-pressure-side bearing and a high-pressure-side bearing which support the shaft portion of the screw rotor, a bearing which supports the shaft portion of the gate rotor, a motor which is directly connected to the shaft portion of the screw rotor and drives the screw rotor, a motor casing which accommodates the motor, and a main casing which accommodates the screw rotor and the gate rotor. Even in the case of the single screw compressor, the steel pipe chamber accommodating the motor casing and the main casing is provided, and the steel pipe chamber is divided in the axial direction so as to form the low-pressure-side chamber and the high-pressure-side chamber. In addition, when the space inside the steel pipe chamber is divided into the low-pressure-side space and the high-pressure-side space through the flange provided in the inner surface of the steel pipe chamber, the flange provided in the main casing or the motor casing, and the sealing component provided between the flanges, it is possible to obtain the same advantages as those of the above-described embodiments.

Further, in the above-described embodiments, the example is described in which the flange provided in the inner surface of the shell 41 and the flange provided in the main casing or the motor casing are connected to each other through the sealing component 30, that is, the flange is disposed on both the ambient air side and the refrigerant side of the shell. However, instead of forming the flange in the inner surface of the shell, even when the flange provided in the main casing or the motor casing is fitted to the flange provided in the outer-surface ends of the low-pressure-side chamber and the high-pressure-side chamber together with the sealing component, it is possible to divide the inside of the steel pipe chamber into the low-pressure-side space 31 and the high-pressure-side space 32. According to the embodiment, it is not necessary to provide the flange of the inner surface of the shell, and thus to more simplify the structure.

According to the above-described embodiments, since the compression mechanism portion is accommodated in the steel pipe chamber, it is possible to remarkably decrease the size and weight of the screw compressor. In addition, the steel pipe chamber is adapted to be divided, and the space inside the steel pipe chamber is adapted to be divided into the low pressure portion and the high pressure portion through the sealing component. Accordingly, in the invention, it is possible to dispose the motor on the low pressure side and to dispose the oil separator on the high pressure side after making the compressor in a semi-hermetic state, which is difficult in the steel pipe chamber structure of the related art. As a result, it is possible to obtain a screw compressor which is small in size and weight and has ease of maintenance and high reliability.

It should be further understood by those skilled in the art that although the foregoing description has been made on embodiments of the invention, the invention is not limited thereto and various changes and modifications may be made without departing from the spirit of the invention and the scope of the appended claims. 

1. A screw compressor comprising: a screw rotor which includes a toothed portion and a shaft portion; a low-pressure-side bearing and a high-pressure-side bearing which support the shaft portion of said screw rotor; a driving motor which is directly connected to the shaft portion of said screw rotor; a motor casing which accommodates the motor; a main casing which accommodates said screw rotor and said low-pressure-side bearing; a discharge casing which accommodates the high-pressure-side bearing of said screw rotor; and a steel pipe chamber which accommodates said motor casing, said main casing and said discharge casing, wherein said steel pipe chamber includes a low-pressure-side chamber and a high-pressure-side chamber which are able to be divided in an axial direction, and wherein a space inside said steel pipe chamber is divided into a low-pressure-side space and a high-pressure-side space through a flange provided in an inner surface of the steel pipe chamber, a flange provided in said main casing or said motor casing, and a sealing component provided between said flanges.
 2. The screw compressor according to claim 1, wherein said low-pressure-side chamber and said high-pressure-side chamber are connected to each other through flanges provided in outer-surface ends thereof, so that the inside of the steel pipe chamber is sealed from an ambient air.
 3. The screw compressor according to claim 2, wherein said high-pressure-side chamber is divided into two parts in the axial direction so as to form a first high-pressure-side chamber connected to said low-pressure-side chamber and a second high-pressure-side chamber connected to the first high-pressure-side chamber, and wherein the first and second high-pressure-side chambers are connected to each other through flanges provided in outer-surface ends thereof, so that the inside of the steel pipe chamber is sealed from the ambient air.
 4. The screw compressor according to claim 1, wherein said flange provided on the inner surface of said high-pressure-side chamber is connected to said flange provided in said main casing through said sealing component, so that a space inside the steel pipe chamber is divided into a low-pressure-side space and a high-pressure-side space.
 5. The screw compressor according to claim 1, wherein said flange provided on the inner surface of said high-pressure-side chamber is connected to said flange provided in said motor casing through said sealing component, so that said space inside said steel pipe chamber is divided into the low-pressure-side space and the high-pressure-side space.
 6. The screw compressor according to claim 1, wherein said flange provided in the inner surface of said low-pressure-side chamber is connected to said flange provided in said main casing through the sealing component, so that the space inside said steel pipe chamber is divided into the low-pressure-side space and the high-pressure-side space.
 7. The screw compressor according to claim 1, wherein said flange provided in the inner surface of said low-pressure-side chamber is connected to said flange provided in said motor casing through the sealing component, so that the space inside said steel pipe chamber is divided into the low-pressure-side space and the high-pressure-side space.
 8. The screw compressor according to claim 1, wherein a central axis of a shell constituting said steel pipe chamber is disposed in a horizontal direction.
 9. The screw compressor according to claim 1, wherein said screw rotor includes at least a pair of male and female rotors meshing with each other.
 10. The screw compressor according to claim 9, wherein an operation fluid to be compressed is a refrigerant used in a refrigeration cycle, wherein a refrigerant having a cooling ability per unit volume flow rate equal to or less than 70% of R407C is used, wherein the number of teeth of the male rotor of said screw rotor is set to four, and the number of teeth of said female rotor thereof is set to six, and wherein the driving motor directly connected to said male rotor is driven by an inverter.
 11. The screw compressor according to claim 9, wherein a central axis of said steel pipe chamber is disposed between a central axis of said male rotor and a central axis of said female rotor.
 12. The screw compressor according to claim 1, further comprising: a gate rotor which meshes with said screw rotor; and a bearing which supports a shaft portion of said gate rotor.
 13. A screw compressor comprising: a screw rotor which includes a toothed portion and a shaft portion; a gate rotor which meshes with said screw rotor; a low-pressure-side bearing and a high-pressure-side bearing which support the shaft portion of said screw rotor; a bearing which supports a shaft portion of said gate rotor; a driving motor which is directly connected to the shaft portion of said screw rotor and drives said screw rotor; a motor casing which accommodates said motor; a main casing which accommodates said screw rotor and said gate rotor; and a steel pipe chamber which accommodates said motor casing and said main casing, wherein said steel pipe chamber includes a low-pressure-side chamber and a high-pressure-side chamber which are able to be divided in an axial direction, and wherein a space inside said steel pipe chamber is divided into a low-pressure-side space and a high-pressure-side space through a flange provided on an inner surface of said steel pipe chamber, a flange provided in said main casing or said motor casing, and a sealing component provided between said flanges.
 14. A screw compressor comprising: a screw rotor; a bearing which supports said screw rotor; a motor which drives said screw rotor; a motor casing which accommodates said motor; a main casing which accommodates said screw rotor; and a steel pipe chamber which accommodates said motor casing and said main casing, wherein said steel pipe chamber is able to be divided in an axial direction, and wherein a space inside said steel pipe chamber which is able to be divided is divided into a low-pressure-side space and a high-pressure-side space through a sealing component. 